This application claims the priority of German Patent Application, Serial No. 100 37 970.2, filed Aug. 3, 2000, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.
The present invention relates to a busbar system for a matrix converter having a number of switching elements, in particular semiconductor switches, which are arranged in a 3xc3x973 matrix.
As is known, a matrix converter includes a self-commutated direct converter which allows a rigid three-phase network to be converted to a system with a variable voltage and frequency. Known matrix converters have a number of electrical switching elements, in particular semiconductor switches (for example Insulated Gate Bipolar Transistors (IGBT)), which are arranged in a switch matrix. The power-electronic switches are arranged in a 3xc3x973 matrix, so that each of the three output phases can be electrically connected to one input phase. On the network side, the matrix converter or the input-side connections is or are connected to capacitor elements, which ensure stable voltage conditions for the switching elements. Since there are three input phases and input voltages, three corresponding capacitor elements are also provided. The connection is made by means of the low-voltage busbar system. Only the presence of the capacitor elements and of the low-inductance busbar system makes it possible for the semiconductor switches in the matrix converter to commutate without excessive overvoltages, so that it is possible to operate an ohmic inductive load, for example a motor. In the matrix converter, three potentials of the input voltage must be connected with low inductance from the input capacitor elements to the semiconductor module which forms the 3xc3x973 switch matrix (or to the modules in a configuration in which the matrix is in the form of three phases which each have modules with three switches).
Conventional busbar systems typically include a plurality of busbar sections, which are arranged in three levels and are isolated from one another, for which purpose appropriate insulation layers are provided between the individual busbar system levels. Overall, this results in a three-layer busbar system. The low inductance is achieved by locating the busbar system levels as close to one another as possible, with the busbar sections having a correspondingly large area.
The conventional busbar system formed with three layers, however, tends to have a high inductance, with the distance between the two outer busbar sections determining the maximum stray inductance. Furthermore, the inner conductor is difficult to cool, since it is largely embedded between the two other busbar sections. In addition, the manufacturing process is complex.
It would therefore be desirable and advantageous to provide an improved busbar system which obviates prior art shortcomings and has a lower stray inductance and a simple design.
The invention relates to a low-inductance busbar system for a matrix converter having a number of switching elements, in particular semiconductor switches, which are arranged in a 3xc3x973 matrix, with the matrix converter being connected on the network side to a number of capacitor elements, via which three input voltage potentials can be passed to the matrix converter. The busbar system has only two layers which are arranged isolated from one another in two levels. The two levels with the various busbar sections can be closely spaced (only the insulating layer is located between them), so that the stray inductance can be reduced even further. The busbar sections forming the respective rail pairs and performing the commutation in accordance with the respective switching state of the switch matrix are appropriately shaped and designed, and are suitably distributed within the levels.
Furthermore, there are no cooling problems since only two conductor levels are provided, which can be easily cooled from the outside. Such busbar system can also be manufactured more easily, since the busbar sections can be applied as flat, metallic conductor layers in a simple manner to an insulating layer of an appropriate size and design. For example, the conductor layers can be in the form of coatings on a board, for example, a printed circuit board (PCB). Safe and reliable processes for coating conductors on PCB are known in the art and can be used to produce the low-inductance busbar system according to the invention.
According to one aspect of the invention, at least one busbar section is provided for each input potential. The busbar sections can be arranged in different ways, depending on the position of the busbar sections in the two levels, while keeping the inductance of the busbar system as low as possible. As discussed below, this can be achieved using a single busbar section for each input potential, or a plurality of busbar sections for one or the other input potential.
According to another feature of the invention, a first large-area busbar section can be provided for the first input potential in the first level, and second and third busbar sections, which at least partially overlap with the first busbar section, can be provided for the second and third input potentials in the second level. Two busbar section pairs, between which the voltage is commutated, are hereby routed alongside one another, with the potentials which are involved in one pair being located one above the other in the two layers. The low-inductance commutation in the third voltage pair, which is located in the second level, is achieved by forming eddy currents in the line routing of the large-area first busbar section in the first level, with the two busbar sections between which the voltage is commutated being arranged alongside each other. Accordingly, a third busbar section is included for this commutation.
For reducing the stray inductance as much as possible, the first busbar section can cover at least 75% of the area of the two other busbar sections. The overlapping area should be as large as possible.
According to another feature of the invention, an associated busbar section can be provided for each input potential in the first level and in the second level. All three possible busbar section pairs between which the voltage is commutated are thereby routed alongside one another, with one busbar section being arranged in the first level, and the other corresponding busbar sections being arranged underneath in the second level. The busbar sections can be arranged such that the respective busbar sections in the first level and in the second level, which form a commutation voltage pair, are located directly opposite one another and overlap with one another over as large an area as possible.
According to another feature of the invention, a busbar section which is associated with the first input potential and a busbar section which is associated with the second input potential can be provided in the first level, and a busbar section which is associated with the second input potential and a busbar section which is associated with the third input potential can be provided in the second level, with the busbar sections being arranged and designed such that the busbar sections which form one commutation voltage pair are opposite one another, or at least partially cover one another. Accordingly, two busbar sections which are each associated with a different input potential can be provided in each level, with one of these busbar sections having a considerably larger area than another corresponding busbar sections. The relatively large area busbar sections which are located in different levels and are each associated with different potentials and furthermore likewise form a commutation voltage pair can then also overlap with one another. The area over with which the busbar sections in each case overlap should essentially be of the same size.
According to yet another feature of the invention, an busbar section can be provided for each input potential in the first level and an additional large-area busbar section which forms an opposing surface can be provided in the second level, wherein the large-area busbar section need not be connected to any of the three potentials and covers the busbar sections of the first level. This feature employs a busbar section which is not connected to any specific potential and which is included in the respective commutation path. The commutation process hereby also takes place by forming eddy currents in the busbar section which forms the opposing surface and is preferably at ground potential. The respective sections are sized so that the live busbar sections completely overlap with the opposite additional busbar section. Alternatively, the additional busbar section can be connected to one of the three potentials.
According to another aspect of the invention, the invention also relates to a circuit arrangement comprising a matrix converter and at least three capacitor elements, which are connected to one another via a low-inductance busbar system of the type described above.
The matrix converter can also be designed to include a plurality of separately configured and arranged output phase modules, which can be connected to the capacitor elements via the busbar system. Thus, the matrix converter is not a central component, but rather includes separate phase modules, for example three phase modules, each of which carries a separate output phase. The busbar system can then be designed so that the capacitor elements make contact with the appropriate phase modules. The phase modules can have a common associated capacitor block, which includes the various capacitor elements and makes contact with the individual modules via the busbar system. Alternatively, each phase module can have its own capacitor block with a plurality of capacitor elements.